1. Field of the Invention
The present invention relates to a circular polarization antenna, a composite antenna having a plurality of antennas including this antenna combined therein, and a receiver, a navigation system, etc. using this antenna, more particularly relates to a circular polarization antenna used for a film antenna used adhered to a transparent windshield etc. of a mobile body such as an automobile, an antenna formed in a transparent windshield of a mobile body such as an automobile, a composite antenna including this antenna, and a navigation system using this antenna.
2. Description of the Related Art
In recent years, along with the mounting of navigation systems into automobiles and other vehicles (mobile bodies), in addition to the antennas for receiving waves such as medium waves (MW) for AM radio, very high frequency waves (VHF) for FM radio and television, and ultra high frequency waves (UHF), high frequency band antennas for global positioning system (GPS), antennas for receiving satellite waves for satellite digital broadcasts and re-radiated waves thereof (gap-filler waves), and antennas for transmitting and receiving waves for telephones such as car phones and mobile phones are becoming necessary for vehicles. Further, for tapping into intelligent traffic systems (ITS), antennas for transmitting and receiving waves with electric toll collection (ETC) systems for automatically collecting highway and road tools and electric beacons of vehicle inembodimention communication systems (VICS) providing traffic inembodimention are becoming necessary. Further, antennas for use in keyless entry systems for remote locking/unlocking of doors, anti-theft systems, remote engine starter systems for remote starting of engines, etc. are becoming necessary. Accordingly, recent vehicles have had to mount antennas for receiving or transmitting many types of waves.
For the waves for GPS, satellite waves for satellite digital broadcasts, or waves for ETC systems among the waves to be transmitted and received by a mobile body, use is made of circular polarized waves. Patch antennas are frequently used as conventional circular polarization antennas. As such a patch antenna, a configuration arranging a planar ground conductor on one surface of a dielectric substrate made of a ceramic or the like and providing a radiating conductor on the other surface is frequently employed. As this type of patch antenna, a low profile type patch antenna used provided on a roof of an automobile or other mobile body has already been proposed. Such a patch antenna is disclosed in for example Japanese Unexamined Patent Publication (Kokai) No. 2002-135045.
However, in the patch antenna disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2002-135045 etc., since a substrate was used, the thickness of the antenna was liable to end up becoming larger, reduction of thickness difficult, and the design of the vehicle impaired. Further, when not providing this patch antenna on the roof of the vehicle, but on the front windshield etc., since a patch antenna must be provided with a substrate and planar ground conductor having at least a certain area, there also exists the problem of degrading the forward field of vision of the driver.
To deal with such problems, as circular polarization antennas not degrading the forward field of vision, circular polarization antennas configured by wire-like conductors such as helical antennas or cross dipole antennas have been proposed, but the antennas of these proposals had the problems that the heights of the antennas became high and phase shifters, signal combiners, and signal distributors became necessary, so the cost became high.